just for additional information, it is seen in concept arts and graphic novel that people in the movie's universe have sort of reinforced shells protecting the brain, at least mercenary people. I'm just sayin' because as it is true the movie got some plotholes, at least this has an explaination (any soldier around here would've jumped to the roof seing that kruger survived a grenade blast to the face) in fact, it was previously imagined that kruger would have had his brain transplanted to a full robotic body at this point.